Magnesium Fluoride MgF2 Evaporation Process Notes
Magnesium fluoride is an inorganic chemical compound with a chemical formula of MgF2. It is white or crystalline in appearance with a melting point of 1,261°C, a density of 3.18 g/cc, and a vapor pressure of 10-4 Torr at 1,000°C. The main application of magnesium fluoride is in optics, due to its distinctive transparency over a wide range of wavelengths. It is evaporated under vacuum to form anti-reflective layers.
Magnesium Fluoride MgF2 Specifications
|Material Type||Magnesium Fluoride|
|Color/Appearance||White, Crystalline Solid|
|Melting Point (°C)||1,261|
|Theoretical Density (g/cc)||2.9–3.2|
|Max Power Density|
|Type of Bond||Indium, Elastomer|
|Thermal Evaporation Techniques||
Boat: Mo, Ta
|E-Beam Crucible Liner Material||FABMATE®, Graphite, Molybdenum|
|Temp. (°C) for Given Vap. Press. (Torr)||10-4: 1,000|
|Comments||Substrate temp and rate control important. Reacts with W. Mo OK.|
* This is a recommendation based on our experience running these materials in KJLC guns. The ratings are based on unbonded targets and are material specific. Bonded targets should be run at lower powers to prevent bonding failures. Bonded targets should be run at 20 Watts/Square Inch or lower, depending on the material.
Empirical Determination of Z-Factor
Unfortunately, Z Factor and Shear Modulus are not readily available for many materials. In this case, the Z-Factor can also be determined empirically using the following method:
- Deposit material until Crystal Life is near 50%, or near the end of life, whichever is sooner.
- Place a new substrate adjacent to the used quartz sensor.
- Set QCM Density to the calibrated value; Tooling to 100%
- Zero thickness
- Deposit approximately 1000 to 5000 A of material on the substrate.
- Use a profilometer or interferometer to measure the actual substrate film thickness.
- Adjust the Z Factor of the instrument until the correct thickness reading is shown.
Another alternative is to change crystals frequently and ignore the error. The graph below shows the % Error in Rate/Thickness from using the wrong Z Factor. For a crystal with 90% life, the error is negligible for even large errors in the programmed versus actual Z Factor.